Allowing children to be picky eaters could make them more prone to allergies.

Mothers have traditionally been told to ‘cocoon’ their children by avoiding high-risk foods during pregnancy and while breastfeeding to protect them from potentially dangerous reactions. But allowing kids to be picky eaters could make them more prone to allergies later in life, scientists have warned.

But now there is a growing belief that the best way to avoid allergic reactions is to meet the problem head-on and expose children to foods like peanuts in infancy.

Three large studies are under way at King’s College London, Cambridge University and Duke University in North Carolina to determine once and for all the best way of protecting against harmful reactions to food.

Prof Gideon Lack, of King’s College, said that until recently mothers were told to breastfeed for up to six months before introducing their babies to other food, and keep them away from possible allergens until the age of two or three.

The idea, he said, was to “wrap the infant up in a sort of immunological cocoon and not expose them to proteins that could launch allergic reactions.

“There is a possibility that we were achieving the reverse of our intentions through this avoidance policy,” he told the Nature journal.

A 2008 study which Prof Lack co-authored suggested exactly the opposite, showing that Jewish children in Britain are ten times more likely to have a peanut allergy than those living in Israel, who eat more foods containing peanuts.

The following year the Department of Health revised its guidelines on allergies to clarify that there is not enough evidence to prove a benefit of restricting the diet of either mother or child from pregnancy to infancy.

The study into peanut allergy being conducted by Prof Lack, along with those in Cambridge and North Carolina, could help explain whether giving children controlled but increasing amounts of peanut-containing foods over time could desensitise them.

Starting in 2006, researchers began following 640 babies, half of whom are judged to be at high risk of food allergies, to see if exposing them to traces of peanuts in their early years causes them to develop adverse reactions.

Previous research at Cambridge has suggested that feeding small doses of peanut flour to allergic children every day for 30 weeks could raise their tolerance to safe levels, enabling most of the group to eat 32 peanuts with no reaction by the end of the trial.

But because studies into allergies have typically followed small groups over brief time periods, there is still no firm evidence over whether desensitising children to foods like peanuts is temporary or permanent.

Hugh Sampson, of the Mount Sinai School of Medicine’s food allergy institute in New York, said: “The biggest thing is not to let mothers feel guilty about whatever choice they make, because at this point we really don’t know the best answer.”